Curable adhesive system

ABSTRACT

PCT No. PCT/GB95/00731 Sec. 371 Date Jan. 9, 1997 Sec. 102(e) Date Jan. 9, 1997 PCT Filed Mar. 30, 1995 PCT Pub. No. WO95/27764 PCT Pub. Date Oct. 19, 1995Two-component curable adhesive for blocking automotive wiring bundles, the respective components preferably amine-terminated polyamide Part A, and acrylate, anhydride or epoxy Part B, being contained in separate sheets which are inter-leaved with one another. The concentration of the reactive components in the sheets is chosen to cause the adhesive to flow on initial heating and then to cure to resist further flow at elevated temperatures in service. Apparatus, kits and method for blocking cables or wire bundles using the adhesive are also claimed.

FIELD OF THE INVENTION

This invention relates to a two-part curable adhesive system, andespecially to such systems which may be very suitable for blockingelectrical cables and harnesses to prevent penetration of fluids betweenthe wires of the cable or harness.

INTRODUCTION TO THE INVENTION

Known blocking adhesives tend to suffer from problems such as inabilityto penetrate adequately into the cable wire bundle, or excessive flowalong the wire bundle, or inability to maintain adequate cable blockingaction when the blocked cable is tested after exposure to temperaturesabove 110° C., for example 3000 hours at 125° C. and 240 hours at 150°C.

SUMMARY OF THE INVENTION

The adhesive system of the present invention provides room-temperaturestability and defines for the first time the "window" of melt flowcharacteristics and controlled speed and level of reaction in the moltenstate, which combine to alleviate the problems of the previously knownblocking adhesives and tend to produce reliable blocking capable ofachieving the aforementioned temperature performance, as hereinafterdescribed.

The invention accordingly provides a two-part curable adhesive systemcomprising Part A material and Part B material, both of which Parts (Aand B) comprise polymeric material and are substantially solid orsubstantially non-flowable at temperatures up to 60° C. and aresubstantially unreactive in contact with each other at temperatures upto 40° C.,

and which Parts (A and B) are capable of flowing and reacting togetherwhen heated in contact with each other to temperatures above 80° C.,preferably within the range from 80 to 150° C.,

the materials of Part A and Part B being selected and proportioned sothat each of the Parts A and B individually has a Brookfield viscosityless than 200 Pa.s at 80° C., and preferably less than 50 Pa.s at 100°C., and preferably less than 20 Pa.s at 120° C.,

and preferably being selected and proportioned so that the viscosity ofeither Part is not more than 2 times (preferably not more than 1.5times, more preferably not more than 1.33) times that of the other partat the same temperature within the range from 80 to 150° C.

wherein material (preferably polymeric material) of at least a firsttype included in Part A carries reactive groups of at least a firstkind, and wherein Part B is substantially free from reactive groups ofthe kind or kinds contained in Part A, and Part B includes material(preferably polymeric material) of the said first type and/or of asecond type (preferably substantially completely compatible with thesaid first type), and wherein material (preferably polymeric oroligomeric material) included in Part B carries reactive groups of atleast a second kind capable of reacting with the said reactive groupscontained in Part A when the Parts A and B are heated together asaforesaid,

and wherein the proportion of the said reactive groups in Part A and/ orin Part B respectively

(a) is at least 45×10⁻⁵ moles (preferably at least 60×10⁻⁵ moles, morepreferably at least 90×10⁻⁵ moles), of the said reactive groups per gramof total material present in the relevant Part,

and

(b) is less than 200×10⁻⁵ moles (preferably less than 150×10⁻⁵ moles),of the said reactive groups per gram of total material present in therelevant Part,

and wherein the reactivity and proportions of the said reactive groupsin Part A and Part B are selected so that, when the Parts are heated toflow and react together, the Brookfield viscosity of the resultingreacting mixture of Part A and Part B

(a) remains below 300 Pa.s

(i) for at least 3 (preferably 4, more preferably 5) minutes at 80° C.,

(ii) for at least 2 (preferably 3, more preferably 4) minutes at 100°C., and

(iii) for at least 1 (preferably 2, more preferably 2.5) minutes at 150°C.

and

(b) rises to at least 1000 Pa.s

(i) within 20 (preferably 10, more preferably 7.5) minutes at 80° C.,

(ii) within 6 (preferably 4) minutes at 100° C., and

(iii) within 3.5 (preferably 2) minutes at 150° C.

DETAILED DESCRIPTION OF THE INVENTION

It is comparatively easy to select materials for making Part A and PartB of the system which are substantially solid or at least substantiallynon-flowable, at temperatures up to 60° C. The materials are alsoselected so that Part A and Part B are substantially unreactive whenplaced in contact with each other at temperatures up to 40° C.

The materials must also be selected, as a first constraint for cableblocking purposes, so that Part A and Part B are capable of flowing andreacting together when heated in contact with each other to temperaturesabove 80° C., preferably within the range from 80 to 150° C. Preferably,the Parts A and B will be capable of thus flowing and reacting attemperatures of 80 to 120° C., more preferably 80 to 100° C., and insome cases especially at 80° C., since these lower temperatures are morelikely to be encountered by the adhesive system when used with aheat-shrinkable covering as hereinafter described. In many cases, it maybe especially preferred that Part A and Part B individually have a lowBrookfield melt viscosity, for example less than 200 Pa.s at 80° C., andpreferably less than 50 Pa.s at 100° C., and preferably less than 20Pa.s at 120° C. (Most commercially used hot melt adhesives tend to haveviscosities of the order of 40-80 Pa.s at 160° C.). Preferably, themajority by weight of the polymeric material in Part A and/or in Part Bhas a flow temperature within the range from 65 to 80° C.

As a second preferred constraint identified by the present invention,the viscosity of either Part A or Part B will not be more than 2 times(preferably not more than 1.5 times, more preferably not more than 1.33times) that of the other Part at the same temperature within the rangefrom 80 to 150° C. Such approximate matching (the closer the better) ofthe viscosities enhances the mixing and reaction of Part A with Part B,especially at the relatively low temperatures and relatively shortheating and mixing times encountered under the aforementionedheat-shrinkable articles.

A third constraint according to the present invention requires thatmaterial (preferably polymeric material) of at least a first type (e.g.polyamide or ethylene/vinyl acetate copolymer or ethylene acrylate co-or ter-polymer) included in Part A carries reactive groups of at least afirst type (e.g. amine groups, hydroxyl groups); that Part B issubstantially free from reactive groups of the kind or kinds containedin Part A; and that material (preferably polymeric material) included inPart B of the said first type and/or of a second type (e.g. ester,epoxy, polybutadienes or urethane oligomers) (preferably substantiallycompletely compatible with the said first type) carries reactive groupsof at least a second kind (e.g. epoxy, anhydride, cyano or acrylategroups) capable of reacting with the said reactive groups in Part A whenthe Parts A and B are heated in contact with each other to temperatureswithin the range from 80 to 150° C. as aforesaid.

A fourth constraint identified by the present invention which tends toenhance blocking performance requires a relatively low level of thereactive groups in one or both of the Parts A and B, so that acontrolled level of reaction is obtained, below that at which thereacted system would be unacceptably brittle or otherwise unsuitable.The proportion of the said reactive groups in Part A, or in Part B, orpreferably in Part A and Part B respectively, is therefore selected oradjusted (a) to be at least 45×10⁻⁵ moles (preferably at least 60×10⁻⁵moles, more preferably at least 90×10⁻⁵ moles), of the said reactivegroups per gram of total material (preferably of total polymericmaterial) present in the relevant part; and (b) to be less than 200×10⁻⁵moles (preferably less than 150×10⁻⁵ moles), of the said reactive groupsper gram of total material (preferably of total polymeric material)present in the relevant Part. At these levels, the reaction can becontrolled to achieve desirable degrees of temperature resistance (e.g.150° C. rating) without detracting from the desired initial flowcharacteristics which tend to produce acceptable levels of blocking.

A fifth constraint indentified by the present invention requiresbalancing of the reactivity of the reactive groups within the aboveranges of proportions in Part A and Part B so that, when the parts areheated to flow and react together, the resulting reacting mixture ofPart A and Part B

(a) remains low enough in viscosity for long enough to permit the moltenmixture to penetrate fully into the interstices to be blocked and tosurround, and to make good surface contact with, the wires or otherelongate members (e.g. optical fibers) within the cable or harness; and

(b) thereafter reacts to a sufficient extent to resist unblocking of theblocked cable or harness when exposed to temperatures up to 150° C., butnot to an extent which unacceptably embrittles the reacted composition.

It has been found, according to the present invention, that this fifthconstraint can be satisfied by selecting the reactivity and proportionsof the reactive groups in Part A and Part B so that the Brookfieldviscosity of the aforesaid reacting mixure

(a) remains below 300 Pa.s

(i) for at least 3 (preferably at least 4, more preferably at least 5)minutes at 80° C.,

(ii) for at least 2 (preferably at least 3, more preferably at least 4)minutes at 100° C., and

(iii) for at least 1 (preferably at least 2, more preferably at least2.5) minutes at 150° C., and

(b) rises to at least 1000 Pa.s

(i) within 20 (preferably 10, more preferably within 7.5) minutes at 80°C.,

(ii) within 6 (preferably within 4) minutes at 100° C., and

(iii) within 3.5 (preferably within 2) minutes at 150° C.

It is possible to select by trial and error, using known test methods,materials which meet the aforementioned five constraints defining the"window" of properties which make the present adhesive system especiallybeneficial for cable blocking. It is believed that any two-part curableadhesive system whose parts are substantially solid and unreactive attemperatures up to 40° C., and which meet the other requirementshereinbefore specified, will achieve superior cable blockingperformance.

The reaction between Part A and Part B, at the relatively low levelswhich achieve the desired high-temperature performance withoutembrittling the adhesive, may involve any appropriate mechanism, forexample polymer chain extension, chain tangling, formation ofinterpenetrating polymer networks, cross-linking, or gel formation.

When gel formation is involved, it is preferred to limit the reactiveproportions so that the weight of gel produced is at least 20%,preferably at least 30%, but preferably no more than 50% of the totalweight of the adhesive system. Lower gel contents, for example 10% or15%, can produce acceptable results, but it is not essential fordetectable levels of gel to be formed if other mechanisms are involved.

The benefits of the present invention may preferably be achieved whenthe aforesaid first type of polymer is polyamide. Polyamides are wellknown, for example those available under the "Macromelt" trade mark,such as M6747, M6301, M6768, M6743 or "Unirez" (Trade Mark) 2654.Mixtures of polyamides may be used.

Preferably, Part A of the system according to the invention comprises atleast 50%, preferably at least 70%, by weight of a firstamine-terminated polyamide, or mixture of such polyamides, having anamine value less than 60, preferably less than 50. Such low-amine-valuepolyamides may be used as the sole polymeric component of Part A. Aminevalues within the range from 20 to 50 (35 to 88 moles per gram),especially 30 to 40 (52 to 70 moles per gram), are preferred, forexample having an amine value of 33. This kind of polyamide isespecially preferred when it has a desirably low flow temperature of 74°C. and a Brookfield melt viscosity of only 25 Pa.s at 100° C.

In many cases, however, it is preferable to blend the majoritylow-reactivity polymer, such as the preferred polyamide just described,with a smaller amount (e.g. at least 5%, preferably at least 10%, byweight of Part A) of a much more highly reactive polymer of the samepolymer type, for example a second amine-terminated polyamide having anamine value greater than 100, preferably greater than 200, morepreferably greater than 300. An example of such a high-reactivitypolyamide is that available under the trade mark Reamide PGF4 fromHenkel which is viscous at room temperature and thus needs theroom-temperature-non-flowable majority polymer to render the blendstorage stable.

The use of a room-temperature-viscous minority polymer of the same or adifferent type is also convenient for adjusting the flow temperature ofthe Part A blend in cases where the majority polymer has ahigher-than-desired flow temperature. It may be desirable that amajority by weight of the polymer of Part A and/or Part B is notflowable at temperatures below 80° C., preferably not below 90° C., andat least 5% of the polymeric material in Part A and/or in Part B isflowable at temperatures of not more than 40° C., and the proportion ofthe flowable polymeric material is selected to reduce the flowtemperature of Part A and/or Part B to less than 90° C., preferably lessthan 80° C., while preferably maintaining the flow temperature(s) above60° C. Preferably, the flowable (at not more than 40° C.) polymericmaterial in Part A and/or in Part B carries a majority of the saidreactive groups in the relevant Part.

Alternatively, the more highly reactive minority polymer could be ofanother type, preferably substantially completely compatible with thesaid first type. This principle of blending a less reactive majoritypolymer with a more reactive minority polymer may be practiced withtypes of polymer other than the preferred polyamide type referred toherein for convenience of explanation. The blending of polymers of asingle type, for example the preferred polyamide type, is believed tohelp in promoting formation of a coherent cured body on reaction of PartA with Part B, thus enhancing the high-temperature blocking performanceof the adhesive.

When a highly-reactive minority polymer is used as described above, themajority polymer may be less reactive than when it is used alone. Forexample the aforementioned first amine-terminated polyamide could havean amine value less than 20, and perhaps as low as, or almost as low as,zero, although a value of greater than 5 is thought desirable. Anexample of such a polyamide would be one of amine value 7-8.

The proportion and kind of reactive groups on the less-reactive majoritypolymer are preferably selected to ensure some degree of chain tanglingor cross-linking or other reaction to enhance the retention of themajority polymers in the eventual cured body of adhesive.

Part B of the adhesive system according to this invention is, asaforesaid, substantially free from reactive groups of the kind or kindscontained in Part A, and includes reactive groups of at least a secondkind capable of reacting with the Part A reactive groups when the PartsA and B are heated together. These Part B reactive groups may be apolymer of the aforesaid first type included in Part B, the use of thesame type of polymer in both Parts enhancing their melt compatibility.Alternatively, or in addition, the Part B reactive groups may be carriedon material (preferably polymeric material) of a second type, preferablysubstantially completely compatible with the said first type.

In many cases, it will be preferred for Part B to include at least 50%,preferably at least 70%, by weight of Part B, of a relatively unreactivepolymer of the said first kind, for example a third polyamide having anamine value not greater than 3, preferably not greater than 1.5, so asto be substantially free of the reactive amine groups found in Part A.This third polyamide is preferably an acid-terminated polyamide.

In this case, Part B will preferably include material, preferablypolymeric or oligomeric material, of the said second type carrying thesaid second kind of reactive groups, preferably carrying a majority orsubstantially all of the second kind of reactive groups. This secondtype of reactive material will preferably constitute from 5 to 30% (morepreferably 10 to 25%, or 15 to 20%) by weight of Part B.

The reactive groups in Part B will be selected to react appropriatelywith the reactive groups in Part A (the Part A groups beingsubstantially absent from Part B). Acrylate, epoxy, anhydride, or cyanogroups are preferred in Part B for reaction with the preferred aminegroups in Part A. Ester or epoxy polymers, or urethane oligomers, arepreferred, although others may be selected from suitably functionalizedprepolymers, for example polyethylenes, polybutadienes, EPDM's,polyamide, or polyethylene waxes. The reactive material may besingle-sited to produce simple chain extension by adding itself to thePart A reactive groups, or may have two or more reactive sides toproduce longer chain extension and/or cross-linking.

It is preferred in some cases that the majority by weight of thepolymeric material in Part A and/or Part B is composed of polymer(s)carrying fewer than 60×10⁻⁵ moles of the said reactive groups per gramof the said majority polymer(s). The said majority polymer(s) in Part Apreferably carry at least 10×10⁻⁵ (more preferably at least 12×10⁻⁵)moles of the said reactive groups per gram of the Part A majoritypolymer(s).

In view of the relatively low levels of reactive groups in the presentadhesive system, it is usually desirable to arrange Parts A and B so asto achieve as much surface contact with each other as practicable beforeheating to initiate the curing reaction. This could be achieved bymixing a powder of the Part A material with a separate powder of thePart B material. However, for cable blocking purposes it is preferred touse a tape or sheet format which can be wrapped around and/or threadedthrough the bundle of wires or fibers to be blocked.

Preferably, a sheet or tape of Part A and a separate sheet or tape ofPart B are formed by coating the Parts A and B respectively ontoseparate release surfaces and solidifiing the coatings, whereafter atleast one sheet or tape of Part A and at least one of Part B are placedin face-to-face contact with each other, preferably after removal of atleast one of them from the release surface on which it was solidified. Acomposite curable sheet or tape which is advantageous for cable blockingcan thus be formed, preferably having at least two sheets or tapes ofPart A in alternating face-to-face contact with a sheet or tape(preferably at least two sheets or tapes) of Part B. The curablecomposition may be supported by a glass fabric or other suitable supportto enhance its strength and handling characteristics during installationin wire bundles or other end uses. Alternatively, either Part A or PartB may be provided in the form of a solid sheet or tape and the otherpart may be extruded or melt coated onto the solid sheet or tape.

Such a composite layered sheet or tape, formed by inter-leavingpreviously solidified layers of Part A and Part B respectively, can besuited especially well to the requirements of cable blocking. Incontrast, sheets formed by compressing the aforementioned mixture of twopowders would tend to be too brittle for blocking purposes; and sheetsformed by partly or wholly melting the mixture of component Parts A andB would tend to react prematurely and thus to reduce the initial flowcharacteristics desired for subsequent blocking end use. Such compressedor melt-processed sheets may tend to be useful where fast reactionand/or a final high level of cure are more important than the initialhigh flow.

The adhesive system of this invention may be carried on a surface of adimensionally heat-recoverable article such that in use the adhesivesystem can be arranged between the heat-recoverable article and anobject about which the article is to be recovered in use, and theadhesive system will be caused to flow and to undergo reaction betweenPart A and Part B by temperatures to which the adhesive system issubjected during the heat recovery of the article.

The invention includes a method of blocking interstices or voids withina cable, comprising placing the adhesive system according to thisinvention in contact with the part of the cable to be blocked, theadhesive preferably being in the form of a tape or sheet wrapped aroundand/or threaded through the said part of the cable, placing an enclosurearound the adhesive system and the said part of the cable, and heatingto cause the adhesive system to flow into the said interstices or voidsand thereafter to react the reactive groups of Part A with the reactivegroups of Part B so as to render the adhesive system substantiallynon-flowable at temperatures up to 150° C.

Preferably, the enclosure comprises a dimensionally heat-recoverablearticle and the said heating is effected by the application of heatwhich causes the said article to recover around the part of the cable tobe blocked. The part of the cable to be blocked in many cases will be ajunction, branch-off, or termination. Blocking at intermediate pointsalong a cable or harness is often required, for example by removing partof a cable or harness sheath, placing the adhesive system around theexposed wires or fibers, and applying a suitable enclosure and heatingto melt and react the adhesive. The blocking adhesive may also beapplied to a harness of wires or fibers before application of an outercovering such as a heat-shrinkable plastics tube.

The invention also includes a kit of parts for cable or harnessblocking, comprising a heat-recoverable article and an adhesive systemaccording to this invention, preferably in the form of a sheet or tapeas hereinbefore described.

In many cases the Part A and Part B components will soften and flow orotherwise fuse over a temperature range and the softeningcharacteristics of the components may be observed by thermomechanicalanalysis (TMA) as described in "Thermal Analysis" by T. Danielspublished by Kogan, Page 1973. Accordingly, the fusion temperature orthe melting point of the reactive components of the adhesive is definedherein as being the temperature at which the TMA probe has penetrated to60% of the total thickness of the material, usually referred to as T₆₀.The TMA data described herein were obtained using a 6.35 mm diameterflat profile loaded with a 50 gram weight and by increasing thetemperature of the material at a rate of 10° C. per minute. Preferablythe temperature at which reactive components of the adhesive initiallybecome soft (referred to as T_(i) on the TMA plot) is not more than 30°C. below and especially not more than 25° C. below the melting point(T₆₀) of the components so that the difference between the maximumstorage temperature and the minimum curing temperature can be reduced asfar as possible.

The level of cure of the adhesive may be measured in a number of ways.For example, it may be measured as an increase in the T₆₀ (as definedabove) or, more preferably the T₈₀ of the adhesive, where T₈₀ is definedas the temperature at which the TMA probe has penetrated to 80% of thetotal thickness of the adhesive. In some cases the composition will curesufficiently to prevent the probe penetrating it by 80% in which casethe total depth of penetration is a better measure of cure. Anothermeasure of the level of cure of the adhesive is its gel content which ismeasured by weighing a quantity of the adhesive into an extractionthimble, refluxing the adhesive for 5 to 8 hours with a solvent (e.g.1,2-dichloroethane or tetrahydrofuran), drying the thimble in an ovenfor 24 hours to evaporate the solvent and, after leaving the driedthimble in the atmosphere for a further 24 hours, reweighing thethimble. The gel content is then defined as the final weight of theadhesive (which is insoluble) expressed as a percentage of the initialweight of the adhesive.

The curable adhesive system may, if desired, consist solely of thereactive components although it may be preferred for it to include oneor more other components mixed with the reactive components. Forexample, Part A may comprise curable resin such as an epoxy resin,preferably one based on bisphenol A or on epoxy novolak resin, and PartB may comprise a curing agent such as an amine, carboxylic acid,phenolic resin or isocyanate curing agent. The curing agent may itselfbe an extrudable polymer, for example it may be a polyamide having freeamino groups or a carboxylated polymer such as an ethylene/acidterpolymer, in which case it need not contain any inert component. Ifthe curing agent is not polymeric, for example an organic peroxide orother free radical initiator, it may be desirable for it to be blendedwith a polymeric material, e.g. a polyester or a reactive or unreactivepolyamide before being formed into the sheet. The Part A curable resinmay, instead, comprise a polyamide having free amine groups, in whichcase the Part B curing agent may comprise a material having free orblocked isocyanate functional groups. e.g. a cresyl-blocked isocyanate.

The polyamides that are most suitable to act as one of the componentsare those that are conventionally used as hot-melt adhesives. Thesepolyamides are characterized by the fact that their amide linkages areseparated by an average of at least fifteen carbon atoms and haveamorphous structures in contrast with the more hightly crystalline,fiber forming polyamides such as nylon 6 or nylon 6.6. The polyamidespreferably have an amine number of at least 1, preferably at least 5.

Chemical curing accelerators may also be present in the curable system,either blended with one of the reactive components or in separateregions of the sheet, provided that they do not unacceptably increasethe rate of cure, thus unacceptably decreasing the flow time of theadhesive. Examples of accelerators include dimethylaminopyridine, tris(dimethylaminomethyl) phenol, tin octoate, imidazole or imidazolederivatives such as salts, substituted imidazoles or metal complexesthereof.

A number of inert components may be incorporated in the compositions aslong as they do not adversely affect the formation of the preferredsheets, and preferably do not affect the increase in rate or level ofcure of the adhesive composition. Also it is preferred that they do notadversely affect the storage life of the adhesive.

Inert components that may be incorporated in the adhesive compositioninclude plasticisers such as phthalates or rosin esters, thermoplasticor thermo-setting polymers, cured or uncured rubbers, inorganicmaterials to modify the properties of the uncured or cured adhesive suchas reinforcing fillers, reinforcing fibres or microspheres, ortackifiers and the like. The other components, whether organic orinorganic, may be in any appropriate physical form, for example they maybe in the form of powder, flake or fibers, and are preferably present inan amount of from 5 to 50 percent by weight based on the total weight ofthe composition. In a preferred aspect of the invention the adhesivecomposition contains one or more other components having a softeningtemperature range (from the initial softening temperature to T₆₀) thatis greater than that of the reactive components so that the softeningtemperature range of the adhesive composition as a whole is greater thanthat of the reactive components, preferably by at least 5° C. This hasthe advantage that, whilst the adhesive will cure when heated to only arelatively low temperature above the maximum storage temperature, itwill possess cohesive and adhesive strength over a significantly greatertemperature range. Alternatively, in some cases where the reactivecomponents have a large softening temperature range it may be desirableto reduce the softening temperature range of the adhesive composition byincorporation of the appropriate components, for example tackifierresins such as hydrogenated rosin esters and terpene phenols or waxes.

As examples of other components that may be incorporated in the adhesivecompositions subject to satisfactory formation of the preferred sheets,there may be mentioned tacky materials such as pressure sensitiveadhesives or mastics, or thermoplastic materials. The other componentsare preferably such as to help the reactive components to mix togetherat the recovery temperature of the recoverable articles with which thecurable adhesive is preferably used.

The preferred curable sheet or tape may be attached to theheat-recoverable article in a number of ways depending on the type ofarticle and curable sheet. For example, where the article has an open,generally uniform configuration, it may be provided with a layer oftacky material, for example a pressure sensitive adhesive layer, e.g. byspraying or in the form of a tape, and the curable sheet may be appliedthereto by application of pressure, pressures in the order of 0.8 MPa(120 p.s.i.) and temperatures of about 15 to 30° C. having been foundsuitable in practice. However, the adhesive system of this invention isoften used as a separate self-supporting sheet or tape for cableblocking purposes.

Specific examples of adhesive systems according to the present inventionwill now be described by way of illustration, percentages being byweight of the whole formulation for Part A or Part B respectively.

EXAMPLE

    ______________________________________    Polyamide I (A.N. 7-8)    74%    Reamide PGF4            17.5%    Foralyn 110              7.5%    Irganox 1010             1.0%    ______________________________________

Brookfield Viscosity 43 Pa.s at 80° C., 12 Pa.s at 100° C.

EXAMPLE A2

    ______________________________________    Polyamide II (A.N. 33)  89%    Foralyn 110             10%    Irganox 1010             1%    ______________________________________

Brookfield viscosity 95 Pa.s at 80° C., 21 Pa.s at 100° C.

EXAMPLE A3

    ______________________________________           Polyamide II    79%           Reamide PGF4    10%           Foralyn 110     10%           Irganox 1010     1%    ______________________________________

Brookfield viscosity 55 Pa.s at 80° C., 14 Pa.s at 100° C.

EXAMPLE

    ______________________________________           Polyamide III   79%           Ebecryl 220     15%           Ebecryl 3605     5%           Irganox 1010     1%    ______________________________________

Brookfield viscosity 64 Pa.s at 80° C., 16 Pa.s at 100° C.

EXAMPLE B2

    ______________________________________           Polyamide III   79%           Ebecryl 220     20%           Irganox 1010     1%    ______________________________________

Brookfield viscosity 60 Pa.s at 80° C., 15 Pa.s at 100° C.

Foralyn 110 (Trade Mark) is a polyterpene tackifier resin from Hercules,which has the unexpected effect of reducing the tack of the Part Aformulations.

Irganox 1010 (Trade Mark) is a well known phenolic antioxidant.

Polyamide III is an acid-terminated version of the aforementionedPolyamide I, having an acid number (A.N.) not greater than 3, preferablynot greater than 1.5.

Ebecryl 220 (Trade Mark) is a hexafunctional urethane acrylate,available from UCB.

Ebecryl 3605 (Trade Mark) is a partially-acrylated bisphenol A epoxyresin available from UCB.

The ingredients of Part A Examples A1 to A3 and of Part B Examples B1and B2 respectively were melt blended in a 2-blade mixer and melt coatedfrom a hopper onto a release surface (silicone-treated paper),whereafter the resulting sheets of Part A and Part B material weresolidified by cooling on the release surfaces.

Layered sheets comprising alternating layers of Part A and Part B werethen prepared by removing the solidified Part A and Part B sheets fromtheir respective release surfaces and laying then successively on top ofone another using a known laminator. In the following Examples,eight-layered latently-reactive curable sheets were prepared using fourlayers of Part A alternating with four layers of Part B in the indicatedcombinations.

EXAMPLE A1B1

Four layers of Part A according to Example A1 (Polyamide I+PGF4)alternated with four layers of Part B according to Example B1(E220+E3605).

EXAMPLE A2B2

Four layers of Part A according to Example A2 (Polyamide II, no PGF4)alternated with four layers of Part B according to Example B2 (E220, noE3605).

EXAMPLE A3B2

Four layers of Part A according to Example A3 (Polyamide II+PGF4)alternated with four layers of Part B according to Example B2 (E220, noE3605).

The omission of the more reactive Ebecryl 3605 (E3605) from Part B wasfound to enhance the storage stability of the layered sheets. Thepresence of the more reactive polyamide Reamide PGF4 in Part A appearedto dominate the rate of cure of the layered sheet at 80° C., whereExamples A1B1 and A3B2 cured faster than Example A2B2. However, at 100°C. and 150° C. the rate of cure appeared to be dominated by thereactivity of the majority polyamide in Part A, with Examples A2B2 andA3B2 curing at much the same rate as each other and considerably fasterthan Example A1B1.

In connection with the aforementioned uses of the adhesive systemaccording to the present invention, it is necessary to considertechniques and equipment for blocking wire bundles, especially wirebundles that are employed in environments where they, or parts of them,may become exposed to water, as a liquid, a spray or as moisture, or toother fluids.

Wire bundles are often employed in wet environments, for example inautomotive applications. The bundle may, for example, extend from theengine compartment where it may be exposed to water, to the interior ofthe vehicle. Not only may the harness be subject to water, but it willnormally be unjacketed, simply having a small winding of tape to hold ittogether, with the result that any water can easily penetrate thebundle. In such a case, and in many others, it may be necessary toprovide the bundle with a water block in order to prevent water ormoisture passing along the wire bundle in the interstices between thewire. A number of arrangements have been proposed for forming a waterblock in such bundles. For example, a system described in Internationalapplication No. WO87/07755 comprises an array of channels formed from ahot-melt adhesive into which wires of the bundle can be located, and adimensionally heat-recoverable sleeve which can be located over thearray. On heating the assembly the hot-melt adhesive forming the arraymelts and the sleeve shrinks in order to produce the final assembly.Although this system generally works very well, problems may occur withvery large numbers of wires in the bundle, for example where there aremore than forty wires. In such a case it may not be possible for theadhesive in the region of the center of the bundle to receive sufficientheat to melt the adhesive fully without heating the outer portions ofthe bundle so much that damage may occur to the wires. For example, inthe case of an automotive harness, the wires may be PVC-insulated wireswhich are rated a temperature of only 85° C. but the adhesive at thecenter of the bundle may require being exposed to a temperature of atleast 95° C. before melting. Although systems employing other forms ofadhesive such as curable adhesives have also been proposed, such systemscan suffer from the problem that insufficient adhesive flows to thecenter of the cable bundle to ensure the blocking of all the intersticesin the bundle, thereby allowing paths for transmission of water alongthe bundle.

According to another aspect of the present invention, there is provideda method of forming a water block in a wire bundle, which comprises:

(i) separating some of the wires in the bundle from others of the wiresin the bundle to form at least one space between them;

(ii) inserting a flexible mass of a curable adhesive (preferably theadhesive system of the present invention) into at least one spacebetween the wires formed in step (i);

(iii) positioning a dimensionally heat-recoverable sleeve over the partof the bundle that contains the adhesive; and

(iv) heating the sleeve and the adhesive to cause the sleeve to recoverand the adhesive to flow into the interstices between the wires and thento cure.

The invention has the advantage that an effective water block may beformed in a wire bundle in a very simple manner and with a relativelyshort assembly time (for example in the order of fifteen seconds). Incontrast, the system described in the application mentioned aboverequires longer assembly times since the wires must be individuallyinserted into the hot melt adhesive profile (array).

The method according to this aspect of the invention can be used to forman effective fluid block, in cases where no such block is formed if themass of adhesive is simply wrapped around the bundle without beinginserted. It is believed that this is partly due to the reduction indistance the adhesive has to flow in order to block the bundle, and ispartly due to the fact that the separation of the wires in step (i)disrupts the layup of the wires to some extent, thereby creating gapsbetween individual wires in the bundle through which the fused adhesivemay flow. In contrast, with known cable blocking techniques employingheat-shrinkable sleeving, recovery of the sleeve would often compressthe wires of the cable bundle and impede flow of adhesive radiallyinwardly to the center of the bundle. In view of this, it is preferredfor the method according to the invention to include the location of afurther quantity of adhesive around the periphery of the wire bundle inaddition to the mass(es) of adhesive that are inserted into the bundlesince the adhesive located within the bundle will often aid flow of theadhesive from the periphery to the center of the bundle. The methodaccording to this aspect of the invention is particularly useful wherethe harness includes a relatively large number of wires, e.g. 20 ormore, and especially 40 to 60 wires although the number of wires may beas high as 100 or even more.

The further quantity of adhesive is preferably in the form of anelongate flexible mass that is wrapped around the wire bundle. Theadhesive may be employed in any of a number of forms. For example it maybe formulated to have the consistency of dough or clay in order that itcan be handled easily and also be conformable to some degree with thecable. Alternatively, the adhesive may be solid or liquid if it issupplied in an appropriate manner, that is to say, if it is flexible.For example the adhesive may be located in one or more flexible bagswhich will allow the adhesive to flow out when it has been heated. Suchbags may, for example, be perforate, for example they may have a numberof slits or they may be fusible at a temperature that will beexperienced during heating of the adhesive. In one preferred method theadhesive is located in a number of sachets that are concatenated to forma train. The sachets may be formed from a material such as anethylene/vinyl acetate copolymer that will melt at a relatively lowtemperature, e.g. in the region of 50 to 80° C., and so will let theadhesive flow out when heated. The flexible mass of curable adhesive andthe further quantity of curable adhesive may be formed separately fromone another and may, in fact, have different compositions. However, itis preferred for them to be the same, and especially for the mass ofcurable adhesive to form part of the further quantity of curableadhesive. Thus, for example, the mass of curable adhesive that isinserted into the bundle may comprise the end portion or portions of along train of sachets of the adhesive that is wrapped around the bundleperiphery; or preferably it will comprise part(s) of the layered sheetor tape of the adhesive system hereinbefore described.

The adhesive may include a component such as an epoxy, preferably onebased on bisphenol A or an epoxy novolak, and a second component orcuring agent which is reactive with the first component to cure theadhesive. Examples of curing agents that may be employed with epoxyresins include amines, carboxylic acids, phenolic resins, anhydrides orisocyanates. As stated above the adhesive may be in solid or liquidform. Where the adhesive is provided in the aforementioned sachets it ispreferably particulate, for example having particles of weight averagediameter in the range of from 1 to 1000 μm, especially 10 to 300 μm. Insuch a case the curing agent may exist separately from the firstcomponent. In this case the curing agent particles may appropriatelyhave a weight average diameter that is substantially the same as that ofthe first component particles. Alternatively the first component may beprovided in the form of a liquid for example if the adhesive is locatedin sachets of impervious material. In such a case it is preferable forthe curing agent to be microencapsulated with an inert microencapsulantthat will disappear, for example will fuse, when the adhesive is heated.

Whatever the adhesive, and whatever form it is in, it advantageouslybecomes relatively fluid for a period of time when it is heated beforecuring sets in and its properties change to those of the cured adhesive.Preferably, the adhesive has a viscosity that falls during heating to aminimum value that is not more than 2.5×10⁴ and especially not more than2×10⁴ centipoise, but which is at least 6×10³ and especially at least8×10³ centipoise. The upper limit for the viscosity range is normallydetermined by the ability of the adhesive to flow laterally throughoutthe wire bundle during heating, adhesives that are significantly moreviscous tending to leave one or more axially extending moisture pathswhere it has flowed insufficiently. The lower limit for the viscosity isdetermined by the undesired tendency of the adhesive to flow along thewires away from the water blocking area, thereby depleting the waterblock of adhesive.

The wire bundle, adhesive and heat-recoverable sleeve will normally beheated by means of a hot-air gun for a period in the range of from 1 to10 minutes in order to fuse the adhesive and recover the sleeve and theassembly will then be left to cool. The maximum amount of heat that maybe applied to the assembly is normally determined by the temperature towhich the wires forming the bundle can be raised without damage, whichis normally in the region of 80 to 160° C. In some instances theadhesive will begin to take on some of its cured properties during theheating stage, but usually this will happen only after heating hasstopped and the assembly is allowed to cool down. It is preferred forthe adhesive to solidify near or at substantially its meltingtemperature, since any tendency of the adhesive to supercool willlengthen the period during which the adhesive is liquid and will delaythe time at which the bundle may be handled. In the case of wire bundlesemployed for automotive applications such a delay can be considerablydisadvantageous from an economic point of view in view of the speed atwhich the vehicle components are assembled.

As stated above, the sleeve is dimensionally heat-recoverable. Usuallythese articles recover, on heating, towards an original shape from whichthey have previously been deformed but the term "heat-recoverable", asused herein, also includes an article which, on heating, adopts a newconfiguration, even if it has not been previously deformed. In theirmost common form, such articles comprise a heat-shrinkable sleeve madefrom a polymeric material exhibiting the property of elastic or plasticmemory as described, for example, in U.S. Pat. Nos. 2,027,962; 3,086,242and 3,597,372. As is made clear in, for example, U.S. Pat. No.2,027,962, the original dimensionally heat-stable form may be atransient form in a continuous process in which, for example, anextruded tube is expanded, whilst hot, to a dimensionally heat-unstableform but, in other applications, a preformed dimensionally heat-stablearticle is deformed to a dimensionally heat-unstable form in a separatestate.

In the production of heat-recoverable articles, the polymeric materialmay be cross-linked at any stage in the production of the article thatwill enhance the desired dimensional recoverability. One manner ofproducing a heat-recoverable article comprises shaping the polymericmaterial into the desired heat-stable form, subsequently cross-linkingthe polymeric material, heating the article to a temperature above thecrystalline melting point or, for amorphous materials the softeningpoint, as the case may be, of the polymer, deforming the article andcooling the article whilst in the deformed state so that the deformedstate of the article is retained. In use, since the deformed state ofthe article is heat-unstable, application of heat will cause the articleto assume its original heat-stable shape.

Any material to which the property of dimensional recoverability may beimparted may be used to form the sleeve. Preferred materials includelow, medium or high density polyethylene, ethylene copolymers, e.g. withalpha olefins such as 1-butene or 1-hexene, or vinyl acetate, polyamidesor fluoropolymers, e.g. polytetrafluoroethylene, vinylidine fluoride orethylene-tetrafluoroethylene copolymer.

BRIEF DESCRIPTION OF THE DRAWINGS

A method according to this aspect of the present invention will now bedescribed by way of example with reference to the accompanying drawings,in which:

FIG. 1 is a view of part of a cable bundle at one stage during themethod;

FIG. 2 is a view of the cable bundle and the mass of adhesive during themethod;

FIG. 3 is a view of the cable bundle later during the method;

FIGS. 4 to 6 are cross-sections through cable bundles showing thedifferent configurations of adhesive mass that can be used; and

FIGS. 7 to 9 show steps of a method for forming a block as shown in FIG.5.

FIGS. 10 to 11 show housings for forming the cable bundles.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to the accompanying drawings, in order to form a water blockin an unjacketed bundle 1 of PVC wires, a length (about 7 cm) ofdimensionally heat-recoverable tube 8 is first placed over one end ofthe bundle and slid to a position adjacent to that where the block isintended to be. The bundle 1 is separated manually into two bunches 2and 3 having a small space between them. A sachet 4, that is formed froman ethylene/vinyl acetate polymer and contains a quantity 5 of a curableepoxy adhesive which contains a microencapsulated hardener, is insertedthrough the said space between bundles 2 and 3. The sachet may be anindividual sachet or may be part of a train 6 of sachets in which casethe train of sachets is inserted into the space between the wire bundlesuntil the middle portion of the train is located between the two bundles2 and 3. Alternatively a single long thin sachet may be employed inplace of a train of short sachets. The remaining parts of the train 6 ofsachets are then wrapped around the cable bundle in the same directionso that the bulk of the adhesive is located around the periphery of thebundle and a quantity is located in the center of the bundle as shown inFIG. 3. The heat-recoverable tube 8 is then slid over the adhesivesachets and the assembly is heated by means of a hot-air gun so thatboth ends are recovered initially, whereupon the tube 8 begins torecover and hold the adhesive sachets in place. The adhesive then beginsto become more fluid and mixes with the curing agent as themicroencapsulant melts, and, as the heating continues the sachets meltthereby allowing the adhesive to flow into the wire bundle (andinevitably, along it to some extent). After 5 minutes the heating isstopped and the assembly is left to cool, whereupon the viscosity of theadhesive increases, partly due to cooling and partly due to curing ofthe adhesive. In about 15 minutes from termination of the heatingoperation the assembly can be handled, for example it can be installedin a vehicle, and after about a day the adhesive will substantially havefinished curing. The configuration of the mass of adhesive is shown inFIG. 4.

FIGS. 5 and 7 to 9 show a modification of the assembly shown in FIGS. 1to 4 after the adhesive sachets 6 have been positioned in place andaround the wire bundle 1. In this modification the wires of the bundlehave been separated into three bunches 2, 3, and 3' and 3" and twosachets 4 and 4' have been inserted between the bunches, one in eachspace. The method is otherwise as described above with reference toFIGS. 1 and 2, but in this case the curable adhesive 5 has a shorterdistance to flow in order to fill the interstices between the wires andblock the bundle.

The following Examples illustrate this aspect of the invention:

EXAMPLE 1

A bundle containing 57 crosslinked PVC insulated wires was split asshown in FIG. 1 and a single adhesive sachet was inserted and wrappedaround the bundle to form the configuration shown in FIG. 4. Theadhesive used was a mixture comprising 70% by weight of amicroencapsulated epoxy imidazole adduct as described in European PatentApplication No. 193068 and sold by Asahi under the designation HX 3722,and 30% by weight of a liquid epoxy sold under the trade name Epikote1002. The sachet was formed from unperforated ethylene/vinyl acetatecopolymer and was 150×25 mm in size, containing 8 grams of adhesive. Thesachet could be applied in 15 seconds and, after slipping theheat-shrinkable sleeve over the sachet, the assembly was then heated tomelt and cure the adhesive.

In order to test the block, after the bundle had cooled it was attachedto a pressurized air line by means of a compression gland, which sealsonto the jacket of the block. A soft rubber seal was used to ensureminimum pressure was placed on the block.

The block was then immersed in water with the wire tails extending fromthe block so that their ends were above the surface of the water. Theblock was pressurized to 0.5 bar. No air leak (ie. bubbles) emerged fromthe block (duration 30 seconds) indicating that the block had passed.

EXAMPLE 2

Example 1 was repeated with the exception that the sachet had dimensionsof 150×10 mm and contained 6 g adhesive, and that the sachet was wrappedabout the bundle using the configuration shown in FIG. 5.

EXAMPLE 3

Example 2 was repeated with the exception that the sachet was wrappedusing the configuration shown in FIG. 6. The time required to apply thesachet was 30 seconds.

The sachets may be replaced by the layered adhesive tape hereinbeforedescribed.

It is preferred that the heating is effected in heating apparatus bywhich the heat is first directed to recover end portions of theheat-recoverable article (sleeve) and thereafter is directed to recoverportions of the heat-recoverable article (sleeve) between the recoveredend portions.

An especially useful form of apparatus for performing the heating step,substantially without relative movement during the heating between theheating apparatus and the heat-recoverable article (sleeve) and otherobjects to be heated, comprises

(a) a housing adapted for positioning around the objects to be heated,incorporating at least first and second channels arranged for alignmentwith the end portions of the said heat-recoverable article (sleeve) inuse and at least a third channel arranged for alignment in use with thesaid portions of the heat-recoverable article (sleeve) between its endportions, and

(b) means for directing heated air through the said at least first andsecond channels at such a temperature and for such time as will recoverthe said end portions, and

(c) means for (preferably thereafter) directing heated air through thesaid at least third channel at such a temperature and for such time aswill recover the said portions between the ends and substantiallycompletely melt the adhesive to flow and thereafter to cure.

Preferably, the channels are formed in two (or more) housing sectionswhich can be separated to permit lateral insertion of the cable or wirebundle and blocking components and can then be brought towards eachother substantially to surround the objects so inserted with thechannels aligned as aforesaid with the heat-recoverable article. It ispreferred to have a source of hot gas (preferably air) and means fordirecting hot gas therefrom selectively first into the end-heatingchannels and then into the central channel(s). It is also preferred tohave a separate source of cold gas (air) with means for directing itinto the outer channels to cool the ends of the blocking assembly aftercompletion of the heating and shrinking of the ends, while still heatingthe central portion. The cooled ends thus help to prevent the moltencentral blocking material from leaking away along the cable while it isflowing and penetrating the interstices of the cable to be blocked. Thisalso has the advantages of reducing the tendency for the sleeve to "milkoff" during heating and of reducing the likelihood of thermal damage tothe wires near the ends of the sleeve. In a form of apparatus where thechannels are provided in two roughly semi-circular separable housingsections, it may be advantageous to provide each of the two sectionsseparately with a hot and a cold gas (air) source and means fordirecting the gases as aforesaid. A preferred form of the apparatus mayinclude any or all of the following features: automatic means forgripping the cable or wire bundle; automatic means for bringing thehousing sections together around the cable or wire bundle and blockingcomponents; automatic means for activating the hot and cold gas (air)supplies (e.g. electrically heated hot air guns); automatic valves orbaffles and/or timers for directing the gases into the appropriatechannels for the appropriate times.

One form of such apparatus is shown schematically by way of example inFIGS. 10 and 11 of the accompanying drawings, wherein

FIG. 10 shows the two housing sections in closed position as they wouldbe around a cable or wire bundle (omitted for clarity); and

FIG. 11 shows one of the housing sections in the retracted position,displaying the aforementioned three channels for directing the hot gas.

In FIG. 10, the two housing sections 10, 12 are positioned together tosurround a cable and blocking components (omitted for clarity) whichwould in use be clamped by clamping means 14, 16 and would projectthrough the encircling housing sections and out of the plane of thepage.

Hot air guns 20, 22, 24 and 26 are connected to inlet holes in thehousing sections, guns 20 and 22 being movable together with housingsection 10 and guns 24 and 26 being movable together with housingsection 12 in the directions indicated by the arrows to separate thehousing sections for convenient lateral insertion of the cable andblocking components. The guns are controlled by automatic means (notshown) to apply the necessary heat for the necessary time first to thetwo outer channels formed within the housing sections and then to theinner channel, as described below. Cold air lines 28, 30 are connectedto inlet holes in the housing sections to supply cooling air, againunder automatic control, to cool the blocked cable after completion ofthe heating operations.

FIG. 11 shows the housing section 12 in more detail. Hot air guns 24 and26 are connected to inlets 34 and 36 respectively in the outer andcentral channels. The hot air guns 20 and 22 in the other housingsection 10 are respectively connected to similar inlets in the outer andcentral channels, so that a larger supply of hot air, from guns 22 and26, is provided to the central channel, where enough heat must besupplied for shrinking the central portion of the heat-recoverablesleeve and for melting the bulk of the curable adhesive system insidethe sleeve. The cold air lines 30 are correspondingly connected toinlets 40 in the outer channels of housing section 12, while the coldair lines 28 are similarly connected to the outer channels of housingsection 10, thus providing a cooling supply to the outer channels only,as aforementioned. Suitable baffles (not shown) may be used to adjustthe air flow to encourage uniform circulation.

This, or similar, apparatus may be used advantageously for blockingautomotive cables and harnesses, preferably with the layered Part A/PartB adhesive system of the present invention, where efficient repetitiveblocking processes are required using external heating.

What is claimed is:
 1. A two-part curable adhesive system for blockinginterstices or voids within a cable or harness, the adhesive systemcomprising Part A material and Part B material, wherein Part A and PartB respectively are in the form of sheet or tape, the adhesive systemcomprising at least one sheet or tape of Part A in face-to-face contactwith at least one sheet or tape of Part B, both of which Parts A and Bcomprise polymeric material and are substantially solid or substantiallynon-flowable at temperatures up to 60° C. and are substantiallyunreactive in contact with each other at temperatures up to 40° C.,andwhich Parts A and B are capable of flowing and reacting together whenheated in contact with each other to temperatures above 80° C., thematerials of Part A and Part B being selected and proportioned so thateach of the Parts A and B individually has a Brookfield viscosity lessthan 200 Pa.s at 80° C., wherein Part A includes material of at least afirst type, and Part B includes at least one material selected from thegroup consisting of materials of said first type and materials of asecond type, and wherein said material of Part A of said first typecarries reactive groups of at least a first kind, and a said material ofPart B carries reactive groups of at least a second kind capable ofreacting with said reactive groups contained in Part A when Parts A andB are heated together as aforesaid, Part B being substantially free fromreactive groups of the kind or kinds contained in Part A, and whereinthe proportion of the said reactive groups in Part A or in Part Brespectively(a) is at least 45×10⁻⁵ moles of the said reactive groupsper gram of total material present in the relevant Part, and (b) is lessthan 200×10⁻⁵ moles of the said reactive groups per gram of totalmaterial present in the relevant Part, and wherein the reactivity andproportions of the said reactive groups in Part A and Part B areselected so that, when the Parts are heated to flow and react together,the Brookfield viscosity of the resulting reacting mixture of Part A andPart B (a) remains below 300 Pa.s(i) for at least 3 minutes at 80° C.,(ii) for at least 2 minutes at 100° C., and (iii) for at least 1 minutesat 150° C., and (b) rises to at least 1000 Pa.s(i) within 20 minutes at80° C., (ii) within 6 minutes at 100° C., and (iii) within 3.5 minutesat 150° C.
 2. An adhesive system according to claim 1, wherein thematerials of Part A and Part B are selected and proportioned so that theviscosity of either Part is not more than 2 times that of the other partat the same temperature within the range from 80 to 150° C.
 3. Anadhesive system according to claim 1, wherein the said first type ofmaterial is a polymer which is polyamide.
 4. An adhesive systemaccording to claim 3, wherein Part A comprises at least 50% by weight ofa first amine-terminated polyamide having an amine value less than 60.5. An adhesive system according to claim 4, wherein Part A includes atleast 5% by weight of a second amine-terminated polyamide having anamine value greater than
 100. 6. An adhesive system according to claim5, wherein the said first polyamide has an amine value of less than 20and greater than
 5. 7. An adhesive system according to claim 4, whereinthe said first polyamide has an amine value within the range from 20 to50.
 8. An adhesive system according to claim 1, wherein Part B comprisesat least 50% by weight of a third polyamide having an amine value notgreater than 3 which is an acid-terminated polyamide.
 9. An adhesivesystem according to claim 1, wherein Part B includes the said secondtype of material which is polymeric, and which carries a majority of thesaid reactive groups in Part B.
 10. An adhesive system according toclaim 1, wherein the reactive groups in Part B are acrylate, anhydrideor epoxy groups.
 11. An adhesive system according to claim 1, wherein amajority by weight of the polymer of Part A and/or Part B is notflowable at temperatures below 80° C., and at least 5% of the polymericmaterial in Part A and/or in Part B is flowable at temperatures of notmore than 40° C., and the proportion of the said flowable polymericmaterial is selected to reduce the flow temperature of part A and/orPart B to less than 90° C., while maintaining the flow temperature(s)above 60° C.
 12. An adhesive system according to claim 11, wherein theflowable (at not more than 40° C.) polymeric material in Part A and/orPart B carries a majority of the said reactive groups in the relevantPart.
 13. An adhesive system according to claim 1, wherein a majority byweight of the polymeric material in Part A and/or in Part B is composedof polymer(s) carrying at least 10×10⁻⁵ and fewer than 60×10⁻⁵ moles ofthe said reactive groups per gram of the said majority polymer(s). 14.An adhesive system according to claim 1, wherein the polymers areselected and proportioned so that each of the Parts A and B individuallyhas a Brookfield viscosity of less than 50 Pa.s at 100° C. and less than20 Pa.s at 120° C.
 15. An adhesive system according to claim 1, whereina majority by weight of the polymeric material in Part A and/or in PartB has a flow temperature within the range from 70 to 80° C.
 16. Anadhesive system according to claim 1, carried on a surface of adimensionally heat-recoverable article such that in use the adhesivesystem can be arranged between the heat-recoverable article and anobject about which the article is to be recovered in use, and theadhesive system will be caused to flow and to undergo reaction betweenPart A and Part B by temperatures to which the adhesive system issubjected during the heat recovery of the article.